At a certain point, opening the downtown apartment doors stops giving it. What should you do then?
Short version, go basically anywhere else.
Long version, most locations have locked doors, about everywhere except public parks, though often only two or three doors/treasure chests.
From the source code
/* daily - returns true if the site type supports high security */
char securityable(int type)
{
switch (type)
{
case SITE_BUSINESS_CIGARBAR:
case SITE_RESIDENTIAL_APARTMENT_UPSCALE:
case SITE_LABORATORY_COSMETICS:
case SITE_LABORATORY_GENETIC:
case SITE_GOVERNMENT_FIRESTATION:
case SITE_INDUSTRY_SWEATSHOP:
case SITE_INDUSTRY_POLLUTER:
case SITE_CORPORATE_HEADQUARTERS:
case SITE_MEDIA_AMRADIO:
case SITE_MEDIA_CABLENEWS:
return 1;
//These places have better quality locks.
case SITE_BUSINESS_BANK:
case SITE_INDUSTRY_NUCLEAR:
case SITE_GOVERNMENT_POLICESTATION:
case SITE_GOVERNMENT_COURTHOUSE:
case SITE_GOVERNMENT_PRISON:
case SITE_GOVERNMENT_INTELLIGENCEHQ:
case SITE_GOVERNMENT_ARMYBASE:
case SITE_CORPORATE_HOUSE:
case SITE_GOVERNMENT_WHITE_HOUSE:
return 2;
}
return 0;
}
That first chunk is a list of locations hard-coded to have locks tougher than a typical apartment. Note: APARTMENT_UPSCALE is usually referred to as Condominium or Condo.
The second chunk is a list of locations where high levels of security are used. They're the reason you want to keep training security as high as possible. They've got the stuff.
If you have a decent amount of in-game currency on hand, the university district can teach security.
ActivityAndString(ACTIVITY_STUDY_LOCKSMITHING,CONST_externallyStoredData273)
it's listed as "Locksmithing"
Once you've got a security master, the teaching skill gains some degree of value.
vector<CreatureTypes> ACTIVITY_TEACH_COVERT_DEFAULT;
// this second block are creatures with Computers, Security, Stealth, Disguise, Tailoring, Seduction, Psychology, & Driving
Ordering a member to teach "covert" includes teaching security. That said, this option is only for those with lots of time and money, because the teaching skill is notoriously tedious to grind.
Hope that helps